amazon web services - AWS S3 Bucket Access from EC2

Question

I need to fire up an S3 bucket so my EC2 instances have access to store image files to it. The EC2 instances need read/write permissions. I do not want to make the S3 bucket publicly available, I only want the EC2 instances to have access to it.

The other gotcha is my EC2 instances are being managed by OpsWorks and I can have may different instances being fired up depending on load/usage. If I were to restrict it by IP, I may not always know the IP the EC2 instances have. Can I restrict by VPC?

Do I have to make my S3 bucket enabled for static website hosting? Do I need to make all files in the bucket public as well for this to work?

Answer 1

You do not need to make the bucket public readable, nor the files public readable. The bucket and it's contents can be kept private.

Don't restrict access to the bucket based on IP address, instead restrict it based on the IAM role the EC2 instance is using.

1. Create an IAM EC2 Instance role for your EC2 instances.
2. Run your EC2 instances using that role.
3. Give this IAM role a policy to access the S3 bucket.

For example:

{
  "Version": "2012-10-17",
  "Statement":[{
    "Effect": "Allow",
    "Action": "s3:*",
    "Resource": ["arn:aws:s3:::my_bucket",
                 "arn:aws:s3:::my_bucket/*"]
    }
  ]
} 

4. If you want to restrict access to the bucket itself, try an S3 bucket policy.

For example:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": ["arn:aws:iam::111122223333:role/my-ec2-role"]
      },
      "Action": "s3:*",
      "Resource": ["arn:aws:s3:::my_bucket",
                   "arn:aws:s3:::my_bucket/*"]
    }
  ]
}

Additional information: http://blogs.aws.amazon.com/security/post/TxPOJBY6FE360K/IAM-policies-and-Bucket-Policies-and-ACLs-Oh-My-Controlling-Access-to-S3-Resourc